Iwatsu 7610 ch2 fault

[RussD]

Hi everybody
I have an Iwatsu 4ch 76 series scope
channel 2 flat lines when you go from 50mv to 0.1v range  (same selector for ch1) trace looks true at mv range, nothing at v range the trace moves up/down as normal just no signal there.
any ideas where the best place to start looking???
it's half analogue and half digital switched by a sawtooth to the crt
I have the service manual on pdf

grateful for any thoughts
Russ

[oldway]

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Iwatsu/iwatsu_ss-7611_7610_7607_7606.pdf

[RussD]

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Iwatsu/iwatsu_ss-7611_7610_7607_7606.pdf

thanks Oldway for your reply think there the same manuals I have
kinda looking for clues where to start looking
it's an analogue scope with digital control so is it control fault or something early on in the analogue stages ? it's a complicated little bugger and i'm not sure at what stage the input voltage levels are set
any pointers would be great

[oldway]

This link is not for you but for the members of this forum ...Do you think somebody will help you without having the service manual? 

P167/329 schematic ch1-ch2 Att: relays 3LR23 or 24 faulty, C35, C37, C37a, C38 or C40 short circuited, R60 or R64 open.

[RussD]

point taken

will have a look in that area and report back

I have replaced all the PSU caps and most of them where shot so I would not be surprised if others further down the line where also dodgy but where do you stop with caps!  replacing the lot would be a mammoth task and likely do more harm than good

anyhoo thanks for the pointers

[RussD]

had a quick look and involves de-soldering a number of connectors to remove this card
I'm thinking as its so difficult to remove I might as well replace all the electrolitic's on board
if there not faulty now they will be any time soon.

[oldway]

That's the reason why I like to say:if you choose to go analog oscilloscope, choose a simple one with mechanical rotary switch, not one with sophisticated digital controls. 

If you want a sophisticated oscilloscope, go for a modern digital oscilloscope.

The solution you chose is the worst possible.

For exemple, I just repaired for a friend an old 1986 (thirty years old) HM605 Hameg and the only problems where bad solders and bad contacts.
It has been easily repaired with contact cleaner spray and a solder iron.

Ready for 30 years more ! 

[TAMHAN]

Now dont be so negative. Iwatsu oscillographs are, in general, excellent - I deeply like my DS-6612A, and hope to get the all digital front panel DS-6121A back in action soon.

So, to cut a long story short: all other channels work except for the one. And the one NEVER displays a signal at any V/Div setting? To me, this stinks like some kind of problem in the forwarding of the signal from the probe to the logic...especially as the "adding" of the offset works.

Lets try this: can you trigger the scope from the struck channel? And yes, you must NOT use auto as that always triggers...but rather norm setting which keeps the screen blank if no trigger signal is sniffed out.

Please, I know that I am flatulent now, but make a list of all deflection settings and whether they work or not.

Tam

[RussD]

Hameg's are great
been my most reliable scopes a dash of switch cleaner is all they need
but every now and then an osd and some extra channels comes in very handy, and  Iwatsu  are well made and would cost a good wedge to replace

[chihaxinh]

Hi RussD

oldway said correct , you need check signal path . OSC to old so electrolytics cap alway fail , pls check every al cap in bypass voltage supply for opamp or active device.

I very like Iwatsu , it's excellant brand name analog oscilloscope !

I don't like one reason it's Japanese product , all active device using Japans semiconductor . So if fail hard to find item 

[RussD]

Thank you chihaxinh

it seems to have developed a power up issue so I will have to repair that too and replace all the electrolytic caps at the same time.

as for parts I have another 7610 I can use as a doner